But Equity argues that cutting the size and pay of the chorus is “cultural vandalism”. The union’s president, Malcolm Sinclair, said the cuts would damage ENO’s artistic integrity, “perhaps irreparably”.

Against a background noise of central London traffic, Sinclair said: “I am an actor and I want to make it clear that the entire theatre community is behind this dispute. If this dispute goes on, the actors will be out. And the directors and the designers and the stage managers. They will be out in force to defend this magnificent chorus.”

Equity gave notice that the chorus would be taking action between 4 and 19 March, which might include protests and refusing overtime. The strike action, for which the vote was unanimous, would be in the first act of four in the new production ofAkhnaten, directed by Phelim McDermott, on 18 March, the last night of its run.

Hilary Hadley, the union’s head of live perfomance, said: “The chorus have no interest in causing economic harm to their own company, which is why the overwhelming majority of the industrial action will be protests.” The final night of the run had been chosen in the hope a settlement could be reached, she said.

ENO hopes to save £664,000 a year by cutting the chorus contracts. It wants to reduce the size of the chorus from 44 to 40 and move it from a 12-month to a nine-month contract, reflecting the reduction in work at ENO’s base, the Coliseum. Equity argues that the contract changes could mean a 39% reduction in chorus members’ pay. ENO says it amounts to 17.5%.

In a statement, ENO said it was “extremely disappointed” that the chorus was going ahead with industrial action “before undertaking serious negotiations”.

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It added: “We are saddened that the action that they have chosen seems specifically designed to cause the utmost harm to both the company and our audience. Their choice to disrupt performances ofAkhnaten will only undermine the pride the whole company has in its amazing work and let down every audience member who has paid to see this show.”

It continued: “We cannot place the future of ENO, one of the UK’s greatest cultural assets, at risk of closure. Any strike action undertaken would significantly undermine the work of all members of the ENO family.”

A letter was delivered by Sinclair to the chief executive of ACE, Darren Henley.

Opera is an expensive art form: it gets just under a fifth of ACE money for national portfolio organisations yet audiences are only 3-4% of theatre live audiences.

ACE issued a statement saying: “We are aware that the ENO chorus has voted in favour of strike action. We understand that this is a challenging and distressing time for the organisation and for the individuals involved. We hope that discussions between ENO and the chorus will continue so that this can be resolved as soon as possible.

“It is up to the ENO to decide how they run themselves; our role is to ensure that we get the best value for the taxpayer’s money by investing in well-run companies who delight audiences with brilliant work.”